I'm developing an application where users will be allowed to create custom fields that are part of a record, in addition to the fields that are provided by default. Users will be able to choose names for such fields, as well as their values of course.

To provide some additional validation, users will also be able to choose the data types of these fields using a drop-down list. Because the software is not specifically geared towards technical users, I'm aiming to use terms that will be recognizable to the widest audience.

For example, "text" vs string, "integer" vs int, "number" vs float... however I'm unable to find a suitable synonym for "boolean". Is this word generally recognized outside of mathematics/computing? How can I convey "boolean" to the widest audience possible?

You maybe want to reconsider "Integer" and "Number" too, I'd vote to label those "Number (no decimals)" or "Number (with decimals)". Actually, it'd be even easier if you just go with "Number" and, technically, always use float. The user will probably not distinguish between the two before he encounters the option to choose one.
–
ChristianDec 3 '12 at 8:33

Learn from Excel, and provide "Number(2 digits)". If your users are truly non-technical, that alone will cover 95% of their decimal needs.
–
MSaltersDec 3 '12 at 12:34

Slider switches with the state written in them are more intuitive. There is an old question about that here somewhere (I remember answering it).
–
Danny VarodDec 2 '12 at 22:43

I'm pretty sure that for this sort of input it heavily depends on the label how intuitive (or not) they end up in a form. Since, in this case, the users will generate the labels themselves, I'm willing to bet they can come up with more intuitive labels for checkboxes. They are just more flexible in terms of what states they may describe than these switches, where the label would have to match the state (are the states "on/off"? "yes/no"? – see Roger's excellent explanation).
–
ChristianDec 3 '12 at 8:39

Edited: After reading some of the newer answers, I have to root for "Yes/No" or "True/False".

When using those, two magical things happen:

The user won't even think of what "dual options" might be, which "states" to offer etc., because this input will only suit a certain kind of question.

This only needs a label, whereas the other options require the label and the possible values to be specified – which means more, and more complex input from the user, resulting in more margin for error/ambiguity.

"Yes or no" is just a special case of "One of a list of Choices" and should not be mixed up with a checkbox. As a matter of fact, we often still see checkboxes implemented with a "yes/no" dropdown, and that makes perfect sense. However, the two are very different in nature as soon as more than two options are required.

Whereas most inputs are straightforward, as soon as it comes to choices things get complex and we have various inputs to choose from that do very similar, or the same, thing in slightly different ways. Consider for example a choice out of this list:

Red

Green

Blue

If its one out of many, we can choose between List Box, Dropdown and Radio Buttons.
It its any out of many, we could use a List Box or a Checkbox List.

Most of the time it depends on the exact phrasing of the label and the number of options to choose from which input works best, but it's actually quite complex coming up with the optimal solution. Imagine Radio Buttons for Country Choice, or a List Box for Yes/No. Both are absurd, yet I have seen both implemented.

To wrap it up:
I'd offer "Yes/No" and, if really, really necessary, "One of a list of Choices" or "Any of a list of Choices".

Also, by using "Yes/No" instead of "Checkbox" you can later decide to use another input (e.g. the already mentioned slider switch) without confusing the user. It's cleaner and "content centered" rather than "function centered".
–
ChristianDec 3 '12 at 9:11

Even some databases have skipped the boolean data type. Technically, a boolean value would still use 1 byte (rather than 1 bit) to optimize memory management and block alignment. Thus you could just as well use an byte-size data type with 256 values.

I did exactly this many years ago for a basic HR system where the users could add their own custom fields to a new user-defined table to store whatever they wanted.

At the time I used the terminology True/False to indicate a dual mutually-exclusive state.
Typically the users where adding information that could be answered as This is true or This is false:

This employee has a Level 2 Welding certificate: True.

Very few users had any problem understanding this terminology, True/False isn't usually considered technical among business users (my audience).
Yes/No may be a better option, it really depends on the terminology in common use among your users.

I have found that "True / False" are well understood outside of the technical world, so I would first try to use that in user testing and then only look for another option only if it turns out that it is causing confusion.

To prove the point, I've just asked a 60 year old non-computer literate teacher of 7 year olds what she would understand by a "true or false question". And her answer showed that she had no difficulty in understanding it.

The problem with using something like On/Off state, or Yes/No field, is that this system model description may not correspond to the mental model of the user. For example if actually the options involved are in/out or up/down or hot/cold, then using the term on/off option may be misleading and inappropriate.

Perhaps something generic like Two state option or Dual option would have a better association in more cases.

However - if your scenario only involves dual states of a certain type - for example all yes/no types of interaction, then do use Yes/No option, or if they are all on/off type interactions then by all means use On/Off option.

I probably wouldn't use the word field in this scenario where you have non technical users. The word option better identifies what is going on.

Note: I was going to suggest Binary option, but was unsure whether binary was a common enough term. I search Google for the term 'binary' and it found About 0b1000110000110000101011000000 results. I'm none the wiser ;-)

There are 10 kinds of people: those who understand binary numbers and those who don't.
–
Juan LanusDec 2 '12 at 18:12

Misuse of true/false for non-true/false questions is a problem that can be caused by lazy developers (e.g. "Does this go up?" yes/no instead of "Which way does this go?" up/down). However, there is nothing wrong with using true/false or yes/no in appropriate cases (e.g. "Do you have pets?" yes/no or "Do you agree with the following statements?" yes/no or true/false).
–
Danny VarodDec 2 '12 at 20:20

Haha, that's a nice Google easter egg! :) Given the case of in/out. hot/cold, up/down, to me the two state option is great and can be easily used in conjunction with icons if enough top/bottom cell-padding allows! :)
–
edgaratorDec 2 '12 at 22:50